Worn rubber tires in the past were sent to landfills. More recently other usages of ground rubber tires have been found. In 2003 nearly 290 million scrap tires were generated in the United States, and almost 80% of those waste tires were consumed in applications for fuel, as additives in civil engineering applications, and other uses.
The waste tire rubber is usually cryogenically pulverized into small micron-sized rubber particles. Cut rubber pieces are also ground in ambient conditions to get powder buffing. Those powdered tire rubbers are usually used as fillers in various low-cost rubber or plastic products. Isolation of the carbon black from tire formulations was tried but such products are not necessarily good reinforcing fillers for a new rubber formulation. Utilization of tire rubber materials for value-added applications would be very attractive not only for the recovery of materials but also to control global pollution.
The tire rubber formulation contains significant quantities of carbon black that is used as reinforcing fillers and abrasive resistance for rubber matrices. High structure carbon black made of clusters of ˜10-100 nm size fundamental particles are used in tire rubber formulations to enhance mechanical properties of the product. Rubber particles do not exist as a single fundamental particle; rather they are fused together during production of black to make aggregates of various structures. Such structures are retained in vulcanized rubber products such as pneumatic tires that contain dispersed phases of carbon black in rubber matrix.